This invention relates generally to removal of gas-borne fine dust, or particulate, or aerosol particles, from gaseous streams. More particularly, it concerns improved method and apparatus for achieving such separation, and employing use of plasma to enhance electrostatic precipitation.
Electrostatic precipitators have been in use for many decades as means for the removal of gas-borne fine dust or aerosol particles. In conventional precipitators the particles become electrically charged by the accretion of ions or electrons on their surfaces. The ions or electrons are usually produced by the creation of a discharge in the gas, in which the particles are entrained or suspended, by the imposition of a high DC electric field. The type of electrical discharge for the production of the ions and electrons which subsequently attach to the particles, is a glow discharge, which is a low current discharge. However; since a glow discharge can become an arc, which is a very high current discharge, it becomes necessary in conventional electrostatic precipitators to carefully control the field strength so as to maintain the discharge just below arcing. Large systems are typically designed to bring the discharge just to arcing and then reduce the field strength, to quench the arc, and then again increasing the field strength, thus repeating the cycle continually. This is not a very efficient or effective way of achieving the production of ions in a gas as it requires complex switch gear; the ionization is produced only in a narrow region, and ozone is usually and undesirably produced because of the arcing. Typically it requires on the order of 1 kw electrical power for 1000 ft.sup.3 /min of gas flow through the precipitator.